Development of the Finnish Height Conversion Surface FIN2005N00

With the new Finnish height system, N2000, came the need for a new national height conversion surface, with which ellipsoidal EUREF-FIN heights, as measured with GPS in Finland, can be transformed into N2000 heights, as measured by levelling. The conversion surface was calculated by fitting a correction surface to the Nordic NKG2004-geoid model using 50 EUVN-DA-points, for which both levelled and GPS-determined heights were available. Polynomial surfaces with varying degrees were fitted to the data, as well as least-squares collocation surfaces using varying parameter values The surfaces were analysed using cross-validation. Collocation surfaces performed better than the polynomial surfaces, resulting in smoother surfaces and better fit statistics. Best results were obtained using a correlation length of 200 km and 2 cm noise level in the least-squares collocation. The resulting surface was added to the NKG2004 geoid model to form the new height conversion surface for Finland: FIN2005N00. The standard deviation of the cross-validation residuals indicates that with the new surface heights can be converted with an accuracy better than 2 cm